1. Field of the Invention
The invention pertains to a method for cleaning a washing device of an offset printing machine, in which the washing device of the offset printing machine, which has at least one spray bar, is removed before cleaning and introduced into a cleaning device. In addition, the invention pertains to a cleaning device for implementing the method. Known washing devices in offset printing machines include the rubber blanket washing device and the counterpressure washing device.
2. Description of the Related Art
An offset printing machine is used to print sheets and usually has several printing mechanisms, from which the printed sheets are sent via a conveyor to a delivery stack. Each printing mechanism consists in the manner known in and of itself of a plate cylinder, to which an inking mechanism and a moistening mechanism are assigned; a rubber blanket cylinder; and a printing cylinder. A washing device for the rubber blanket is assigned to the rubber blanket cylinder, this device being located before—with respect to the cylinder's direction of rotation—the contact point with the printing cylinder. This rubber blanket washing device serves to wash the rubber blanket after a certain number of impressions to remove ink residues, paper dust, and other dirt particles.
Permanently installed rubber blanket washing devices are subject to wear and are relatively complicated to maintain and to clean. For this reason, rubber blanket washing devices were developed which can be removed as a unit from the printing machine and cleaned and maintained outside the printing machine. A process for the easy removal and reinstallation of rubber blanket washing devices is disclosed in U.S. Pat. No. 6,308,627.
An example of removable rubber blanket washing device is described in DE 37 44 800 A1. This device consists essentially of a wiping cloth, which can be pressed against the rubber blanket cylinder. The wiping cloth, which can be moistened by a moistening device, can be unwound from a first winding shaft and then wound up on second winding shaft after use.
Modern washing devices which can be laid against the rubber blanket of the blanket cylinder have at least one brush roll, to which water and washing liquid can be supplied by spraying devices. A collecting tank is provided underneath the brush roll.
According to the state of the art, these types of blanket washing devices are cleaned by first removing the unit comprising the blanket washing device from the printing machine, by disassembling it into its essential components, and by cleaning these components in a cleaning tank with flat fine-bristle brushes and coarse-bristle brushes and conventional cleaning agents. These manual cleaning processes make it possible to clean the rubber blanket washing device satisfactorily.
The problem, however, is the large amount of time which this process requires, namely, about 3–4 hours. This time adds up especially in the case of the large, multicolor printing machines with numerous printing mechanisms, each with its own rubber blanket washing device.
The cleaning of the spray bars of modern rubber blanket washing machines, which are provided near the brush rolls to supply the water and cleaning agent, also presents problems. When the rubber blanket washing device is put into operation, it is impossible to prevent small quantities of ink residues, paper dust, and powder from getting into the inside of the spray bars and adhering to the inside walls. The attempt has been made to rinse out the sensitive spray bars with water or compressed air. The cleaning results, however, have been unsatisfactory for the most part. The cleaning efficiency of the rubber blanket washing device, however, depends to a large degree on the satisfactory function of the spray bars.
A process for removing the stencil coatings of screen-printing forms is also known from EP 0 903 230 A2. The screen-printing form along with the stencil carrier is immersed in a liquid bath and decoated by an ultrasound device. The ultrasound device is placed against the stencil carrier, so that there is direct contact between the ultrasound device and the screen-printing form.
Finally, a cleaning tank for the ultrasonic cleaning of printing cylinders of various sizes is known from U.S. Pat. No. 5,291,827. The printing cylinder is rotated continuously in the cleaning liquid as it is being cleaned. The ultrasonic waves have power of about 2,400 watts and a frequency of 27 kHz.